In the middle of a deepening crisis, Madagascar is a country with a new currency - fuel.

Hundreds of thousands of litres are being moved around the island in everything from huge metal drums to plastic soft drinks bottles - by boat, by hand, by truck or by plane.

Roadblocks placed by politicians and run by factions of the deeply divided military have set in motion a massive black-market machine that is driving the country steadily towards lawlessness.

The island's only oil refinery is closed, the stocks are almost dry. The whole fuel business has been driven into an underground world of bribery and corruption.

In Antananarivo, you have to pay anything from $3.50 to $4 a litre, that is if you can find any at all, but on the coast you can buy a litre for less than 40 cents.

Sailing boats

It does not take a mathematician to see that it is very easy to make an awful lot of profit if you have the contacts and the cash to move fuel through blockades put in place by supporters of the old regime of Didier Ratsiraka to isolate the capital and pressure the newly appointed President, Marc Ravalomanana.

I followed the diesel trail from the coast to the capital, on trucks through roadblocks and checkpoints, and by hand over barricaded bridges.

Fresh fruit goes north, fuel comes south

The starting point was Mahajanga, the second largest port in the north-west of the island.

It has been a while since petrol was delivered there, but now a new system is in place.

About three miles off the coast a boat laden with fuel, which rumour says comes from South Africa, is illegally moored and ready to sell in bulk to anyone prepared to make the trip.

Dhows, small traditional sailing boats, make the risky journey. Some people have already been killed trying to return to the shore in overloaded vessels.

Check-points

In Mahajanga, the petrol pumps are empty, but the black-market traders sell for 2,500 Malagasy francs, about 35 cents, a litre.

But there is not a huge amount of fuel available in the town. Most goes into barrels and heads down the road to Antananarivo, 550km (345 miles) and 22 hours to the south.

Ravalomanana's capital is being blockaded

Following the route by "taxi-brousse", the minibuses providing cheap road travel around Madagascar, there are various check-points along the way.

The soldiers armed with a mixture of weapons, from Kalashnikovs to rusty World War I issue rifles.

They check thoroughly for fuel, not necessarily to prevent its movement, more to ensure an appropriate "tax" is paid to allow passage.

The next stop on the road is around 200km (125 miles) out of Mahajanga, at the long metal bridge crossing over the huge rapids of the River Betsiboka, the main blockade on the route.

You can tell you are getting near when you reach the queue of hundreds of trucks lined up along the road waiting to have its cargo transferred across the river.

This is not a blockade to stop goods getting through - it is where the money is made.

'Border town'

Everything gets past the military roadblock, including thousands of barrels of petrol. It just takes time and money.

No vehicles can pass; the military makes sure of that, as does the metal platform welded across the bridge to stop all traffic. But most goods are carried over the kilometre-long petrol-soaked metal bridge to pick up the onward "taxi-brousse".

Ratsiraka refuses to stand down

The atmosphere is like a border town.

Wood and palm-leaf shacks selling food and supplies line the road, and porters clamber for the job of carrying goods across the bridge.

Fuel, flour and sugar moves towards Antananarivo, and in the other direction go fruit and vegetables, rum and empty barrels ready to be filled up for another trip south.

The soldiers on the scene are far from professional. One was chided by a woman for smoking, just metres from where petrol was being siphoned from one vessel to another.

They laze around barking orders and searching people as they pass, just there to ensure the "tax" is paid.

They answer to the provincial governor, a Ratsiraka man, and a lot of money changes hands to ensure a safe passage of valuable cargo.

Gangsters

By the time the barrels cross the bridge they are worth 9,000 Malagasy francs, $1.20 at the black-market exchange rate.

From there to Antananarivo there are more checkpoints, run by armed soldiers answering to who knows who - it is impossible to tell.

Fuel is the new currency

The bribes are paid and the fuel continues its journey.

The "taxi-brousse" arrives on the outskirts of the capital at 0100. Some petrol is sold on the way, but it is too risky to enter the city after dark because of gangsters.

They park up and wait for first light.

In Antananarivo, fuel is sold for between 12 and 14,000 Malagasy francs a litre, $1.75. The people you see in the street siphoning off the precious liquid into cars and vans pay even more.

Ordinary consumers pay at least double.

The political crisis has produced a whole new trade in fuel, becoming more entrenched as the deadlock continues. The longer it goes on, the more money will be made and the more difficult it will be to bring the illegal trade to an end.